The island itself was long and narrow, a little over ten miles in length. At its northern end, sharp rocks split the waters of the Anduin in a bubbling foam that gave the island its name. Cair Andros was covered with trees for much of its length.

Strategically, the island was of immense importance: apart from the bridge at Osgiliath, it was the only practical means for an army from the east to cross the Anduin into Gondor's heartlands. The Gondorians took this risk seriously. Amon Dîn, the first of the Beacon-hills, was set up originally to warn the citizens of Minas Tirith if Cair Andros was ever breached.

Gondor took steps to fortify the island, too, but the history of these fortifications is difficult to establish. We know that it was 'manned' at the time of KingOndoher's fall in III 1944, but whatever defences were in place at that time were apparently abandoned, since Denethor's great-grandfather Túrin II found it necessary to fortify the island again in about the year III 2900.

They retreated to Cair Andros, and apparently held the island for some days. In his march on Mordor, Aragorn released a small group of soldiers from his main army to retake the island if necessary, and hold it. They must have succeeded, since the last we hear of the island of Cair Andros, its moorings were used by the ships of Gondor, as glimpsed by Frodo after completing his Quest.

Notes

1

Tolkien explains the island's name in the Appendices to The Lord of the Rings: '...the isle was shaped like a great ship, with a high prow pointing north, against which the white foam of Anduin broke on sharp rocks.' (The Lord of the Rings Appendix A I(iv), The Stewards.)